MAC-545496 is a nanomolar glycopeptide-resistance-associated protein R(GraR) inhibitor with strong binding affinity to the full-length GraR protein (Kd?≤?0.1?nM). MAC-545496 can reverse β-lactam resistance in methicillin-resistant strains and synergize with CAMPs. MAC-545496 shows remarkable activity in macrophages and attenuates S. aureus virulence in a G. mellonella larvae infection model.
MAC-545496 shows inhibition of mprF expression in a concentration-dependent manner; the half-maximal inhibitory concentration (IC50) is 0.0376??g/mL—matching with the concentration range of the synergistic effect with cefuroxime. MAC-545496 only inhibits the citrate-induced biofilm formation in the wild type in a concentration-dependent manner, suggesting additional potential as a lead for drug discovery. Treatment of S. aureus-infected macrophages with different doses of MAC-545496 added 30?min after phagocytosis shows that the MAC-545496 halts S. aureus replication within macrophages starting at 0.5??g/mL.[1].
MAC-545496 activity is evidenced by increased survival of the drug-treated larvae as compared to infected untreated ones. This corresponds to concentration-dependent killing of S. aureus in the hemolymph of the larvae observed from the CFUs recovered from the hemolymph 200?min after infection. This matchs with the attenuated virulence of the graR::Tn mutant relative to the wild type in Galleria. Treatment with MAC-545496 recapitulates the phenotype of ΔgraR and ΔgraS mutants, effectively inhibiting intracellular S. aureus growth.[1].
[1] El-Halfawy OM, et al. Nat Chem Biol. 2020;16(2):143-149.